The role of the chi1 gene from the endophytic bacteria Serratia proteamaculans 336x in the biological control of wheat take-all

Take-all, a disease caused by the fungus Gaeumannomyces graminis var. tritici, is the most important root disease of wheat and causes severe yield losses worldwide. Using microorganisms as biological agents to control the disease is important because no resistant cultivars or effective chemical fungicides are available. In this study, we tested the biological control capability of a chitinase produced by the endophytic bacterium Serratia proteamaculans 336x against wheat take-all. The chitinase gene chi1 of S. proteamaculans 336x was cloned and heterologously expressed in Escherichia coli. The recombinant protein exhibited chitinase activity and in vitro antifungal activity against G. graminis var. tritici. With in-frame deletion of the chi1 gene by homologous recombination, the chi1-deleted mutant was devoid of chitinase activity and the biocontrol efficacy was reduced by 42.5%. The complementation of the Delta chi1 mutant strain by the chi1 gene resulted in the partial restoration of the chitinase activity and biocontrol efficacy. These results support a role for the Chi1 protein in the biocontrol process of S. proteamaculans 336x against wheat take-all.